The Big Bang theory has been the most widely accepted explanation about how our universe all began — but now experts are challenging the theory.

Brazilian physicist Juliano Cesar Silva Neves claims the Big Bang never happened some 13.8 billion years ago saying the universe may have been preceded by a contraction phase.

The Big Bang theory states the universe started with a small singularity then stretched and expanded over billions of years to the cosmos that we know today.

But Neves believes in the Big Bounce theory in which the universe collapses on itself giving way to an eternal succession of universes.

The researcher, from the University of Campinas’ Mathematics, Statistics & Scientific Computation Institute in Sao Paulo, said: “In order to measure the rate at which the Universe is expanding with the standard cosmology, the model in which there’s a Big Bang, a mathematical function is used that depends only on cosmological time.”

“Eliminating the singularity or Big Bang brings back the bouncing universe on to the theoretical stage of cosmology.”

“The absence of a singularity at the start of spacetime opens up the possibility that vestiges of a previous contraction phase may have withstood the phase change and may still be with us in the ongoing expansion of the Universe.”